test: let the mock hold the world, instead of building it here

[fcsouza]

Two test files stubbed game.items by hand, because the mock's was an empty array and the code under test walks the collection. tests/export.test.ts also stubbed game.journal down to a single find.

@vttforge/testing 0.14.0 makes those real collections and takes the documents as options, so both stubs are gone:

restore = withMockFoundry({ user: { isGM }, items: items() }).restore;

asUser in the API test drops from nine lines to two. Same fixtures, same 31 tests.

This is the third round of the same loop: the module needed something, the mock did not have it, the SDK grew it, and the module deleted the workaround. The stubs it deletes here are the ones written two PRs ago when the code started walking game.items instead of filtering it.

pnpm run typecheck is clean and the 31 unit tests pass.